覆盖JTextField中的paint方法以绘制文本

Question

I am wishing to draw a number onto a JTextField by overwriting the paint method. So that when the user edits the text field the number doesn't disappear. However, at the moment, the number isn't appearing at all, I have tried:

public void paintComponent(Graphics g) {  
     super.paintComponent(g);
     if(number != 0){
            g.setColor(Color.RED);
            g.drawString(String.valueOf(number),0,0);
     }  
}  

Any ideas, is this even possible?

Answer 1

Try to play with Y position in the g.drawString(String.valueOf(number),0,0); call. Eg use getHeight()/2

Answer 2

..when the user edits the text field the number doesn't disappear.

As pointed out by @mKorbel, there is no need to override a JTextField in order to get red numbers, simply configure it using the public methods. OTOH..

g.drawString(String.valueOf(number),0,0);

If this is really all about numbers, perhaps the best approach is to use a JSpinner with a SpinnerNumberModel , and set a custom SpinnerUI .

Answer 3

maybe there no reason override paintComponent() for JTextField , instead of use

• JTextField.setBackground()

• JTextField.setForeground()

• JTextField.setFont()

• JTextField.setHorizontalAlignment(javax.swing.SwingConstants.LEFT)

• some hacks are possible by put there Html colored or special formatted text

EDIT

maybe this question is about

• filtering KeyEvents in the Document / DocumentListener

or

• JFormattedTextField with Number Formatter

Answer 4

Why don't you just add a small JLabel to the front of the JTextField ? The JLabel could contain the number, and because it isn't editable it will always be there no matter what the user changes in the JTextField . You could also format the JLabel to make it red by calling setForeground(Color.RED); . This might be a much simpler solution?

For example, instead of doing this...

JPanel panel = new JPanel(new BorderLayout());
JTextField textfield = new JTextField("Hello");
panel.add(textfield,BorderLayout.CENTER);

You might do something like this...

JPanel panel = new JPanel(new BorderLayout());

JTextField textfield = new JTextField("Hello");
panel.add(textfield,BorderLayout.CENTER);

JLabel label = new JLabel("1.");
label.setForeground(Color.RED);
panel.add(label,BorderLayout.WEST);

Which adds a red JLabel to the left of the JTextField , and because you're using BorderLayout for the JPanel then it automatically makes the JLabel the smallest it can possibly be.